Process for catalytic desulfurization and reforming of cracked naphthas



Oct. 13, 1959 H. F. POLL PROCESS FOR CATALYTIC DESULFURIZATION AND REFORMING OF CRACKED NAPHTHAS Filed March 26, 1956 @avan/ff vri/Wal. Kairi/@.44

UnitedStates Patent PROCESS FOR CATALYTIC DESULFURIZATION AND REFORMING OF'CRACKED NAPHTHAS Harry F. Poll, Fullerton, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March 26, 1956, Serial No. 573,837

9 Claims. (Cl. 208-54) This invention relates to a combined process for desulfurizing and reforming thermally cracked, high-sulfur naphthas to obtain maximum yields of high-octane, lowsulfur naphthas. Briefly, the process includes the following steps:

(1) Fractionating a full-range, thermally cracked naphtha to obtain a light C-C6 fraction substantially free of thiophene sulfur, and having an ASTM maximum boiling point between about 170 and 200 F.;

(2) Subjecting the light fraction to caustic washing or other suitable treatment for the removal of mercaptan sulfur;

' (3) Treating the heavy naphtha fraction from step 1 with hydrogen in a catalytic hydrodesulfurization zone containing a cobalt molybdate catalyst to eifect substantially complete desulfurization;

(4) Treating the desulfurized product from step 3 in a catalytic reforming zone inthe presence of hydrogen to elfect a substantial improvement in octane rating thereof; and

(5) Blending portions of the caustic-treated, low boiling fraction from step 2 with a portion of the reformed product from step 4. It has been found that by splitting the feedstock as outlined iu step 1, and treating the'two fractions separately as described, the reblended product, is (1) higher in octane rating than if the total feedstock were treated un- Vder like conditions by catalytic hydrodesulfurization and reforming, and (2) lower in sulfur and higher in octane rating than if the entire stock were treated by the caustic washing of step 2, followed by reforming. These advantageous results stem in part from the speciic nature of the feedstock which is treated in the fractionation step 1. \It is known that the gasoline fractions produced by thermal cracking of high-sulfur, naphthenic crudes contain both mercaptan sulfur and the more refractory types containing thiophene rings. It has been found that a large portion of the mercaptan sulfur occurs in the low boiling fraction of these naphthas, and that upon fractional distillation the thiophene type compounds, which are not removable by caustic treating, are almost wholly retained in the high-boiling fraction, even though thiophene, and thiophene azeotropes of hydrocarbons present in the feed, may individually boilsubstantially `within the distillation 'temperature range of the overhead fraction.

The principal object of the invention is toeffec't an overall desulfurizing and reforming of thermally cracked, high-sulfur gasolines to obtain maximum yields of highoctane gasoline, or conversely maximum octane rating at a given liquid yield. A specic object is to avoid the treatment in the desulfurizer and the reformer of the low boiling portions ofthe feedstock, inasmuch as these portions are not improved,and may be degraded, by catalytic reforming. Another object is to utilize to the most economical advantage the treating capacity of any given reforming and desulfurizing installation by avoiding the treatment therein of materials not benefited. A still further object is to avoid the hydrogenation of high antiknock olens present in the low boiling portions of the feedstock. A still further object is to minimize,I in a catalytic reforming-catalytic desulfurization combination, the hydrogen consumption in the desulfun'zer, thereby minimizing the portion .of straight run gasoline which must be treated in the reformer in order to produce suflicient hydrogen to supply the desulfurizer. A specific object is to provide means for fractionating high-sulfur, thermally cracked naphthas whereby an overhead fraction containing the bulk of the C5 and C6 hydrocarbons may be obtained, while excluding therefrom'any substantial amounts of compounds containing thiophene rings. Other objects and advantages Will be apparent from the more detailed description which follows.

It is well known in the art that -most catalytic reforming processes do not benefit all portions of the feedstock to the same degree. Specifically, it is known that materials such as cyclohexane, methyl cyclopentane, and oletins boiling in the same range are better excluded from the reformer feed.V The benzene produced by dehydrogenation of cyclohexane and the isomer-ization and dehy-` drogenation of methyl cyclopentane has va lower 1 antiknock value than the original cyclohexane or methyl cyclopentane. The oleiins'will be largely converted `'to parains having a lower anti-knock value than the original olens. For all these reasons it has sometimes been considered desirable to remove such low-boiling materials from the reformer feed.

However, the picture is changed when one considers a naphtha feedstock derived by thermal cracking vof high sulfur crude oils, and which must be desulfurizedprior to reforming. Such naphthas may contain from about 0.5% to 6% by weight of total sulfur, and such sulfur is normally distributed as both mercaptans and cyclic Vcompound such as thiophene. The thiophene-ring compounds are particularly prevalent in thermally cracked naphthas, including coker distillates. Thiophone boils at 183 F., while cyclohexane boils at 177 F. Other hydrocarbons are present which boil very close to these materials. lt would hence appear extremely doubtful whether any significant portion of the C-'C hydrocarbons could be recovered by simple distillation without Acarrying along considerable amounts of thiophene and methyl thiophenes. The methylthiophenes boil at about 23422409 F., and the presence of their azeotropes in the 11G-180 fraction might be expected. 'It has been found however that Vthe thiophene/methyl thiophene/hydrocarbon distribution in the naphthas herein treated is such that an overhead fraction may be separated containing a major portion of the C5 and C6 hydrocarbons, including cyclohexane and methyl cyclopentane as well as like-boiling olens, while the sulfur compounds recovered in said fraction are typically 85-99 mole-percent mercaptans. In the original cracked naphtha, the thiophene type compounds usually predominate, making up from; about 5 0-90 mole-percent of the total sulfur. Fortuitiously, the particular desulfurization process herein describedis well adapted for the selective hydrocracking of thiophene-type compounds. This is an important consideration, because 1% by weight of thiophene sulfur may correspond to about 5-10 volume-percent of the liquid feed. By cata.- lytic hydrocracking, the valuable hydrocarbon residues of the thiophene compounds are preserved in the feed thereby increasing the liquid yield. The lower mercaptans which go to the caustic extraction step however genf erally make up al negligible proportion by volume of the Patented Oct. 13,- 1959` 3 point of` about' 1606-200" F., and still be substantially free of thiophene sulfur, on a debutanized basis. This overhead product, which may initially contain as much as 1.0% of total sulfur by weight may then be treated by solvent' extraction, with for example caustic-methanol- Water, to` produce an essentially doctor sweet product containing 07.0005% of mercaptan sulfur or less, and from about 0.017% to0.08% of total sulfur. The original naphtha feedstock may contain from about 0.2% to 3% by weight of total sulfur. By extracting the overhead withcaustic-meth'anol-water, a sweetened product is obtained? in about 99% liquid yield, having an octane rating of about 95-100 (plus 3 ml. TEL). The same fraction subjectedI to' catalytic reforming under conditions herein described would give about the same liquid yield of aproduct having an octane number of 85-90 (plus 3 ml. TEL).

The details' of the processing may be more readily comprehended'in'connection with the accompanying flowsheet which illustrates one specific modification for carrying out the process. However, it is not meant to exclude other modifications.`

The initialy feedstock, comprising for example a highsulfur,.reduced crude oil is-preheated to a suitable coking temperature, and admitted via line 1 to a thermal coker 2,. of any suitable conventional design for converting petroleum oils to gases and vapors boiling below a particular end point and producing a solid residue of coke. Such coking unit may be of the delayed coking type wherein coke is accumulated during a coking period of 1'5V minutes to 2 hours, for example, and is then removed by suitable means such as with a streamof high velocity water. In such cases coker 2 represents one of several coking units which are employed in sequence for coking and decoking whereby a continuous ow of feed and products may be maintained. In another modification coker 2 may be of the continuous type wherein the oil is continuously passed through a bed of heated pellets of coke or other solid heat transfer material, thereby depositingV a layer of coke upon such pellets. In general such coking operations are effected at relatively low pressures such as in the range of atmospheric to 100 p.s.i.g., while temperatures may range between about 800 and Coke is removed from the coker 2 through line 3. The coker distillate is removed through line 4, whence it is condensed, and passed into a stabilizer-fractionater 5, wherein light gases including methane, ethane and propane are removed overhead through line 6 for any desired subsequent utilization. The bottoms from stabilizer are then transferred via line 7 to a naphtha-fractionating column 9. Fractionating column 9 discharges gasoline-boiling range material, having an end boiling point between about 380 and 460 F. through line 10. Coker gas-oil is taken off as bottoms through line 11, and preferably transferred to a thermal cracking unit 12, which is operated under sufficient temperature and pressure to effect at least a partial cracking of the heavy gas-oil owing therethrough. Normally, a substantial additional yield ofgasoline may be obtained by subjecting the coker gasoil to thermal cracking. The products from the thermal cracker are then taken off through line 13,v and admitted to' a stabilizer-fractionater 14 from which light gases are taken overhead via line 1S. The bottoms product is then tlrnsfe'rred via line 17' to naphtha fractionating column The gasoline boiling range stock from the cracking operation is withdrawn overhead from fractionating column 18 through line 19, and is blended with the coker naphtha in line The combined streamv then flows; throughline 20 into` a dehexanizer column 21. The feed stream admitted' to column 21 through line 20 will normally have an initial boiling point of around 75 85 F and an end boiling point between about 380-460 F.

In dehexanizer column 214 the critical separation of thiophene-free overhead from Cs-C-lean bottoms is accomplished. This column is ordinarily maintained at atmospheric pressure but slightly reduced or superatmospheric pressures may be employed. The factors of reilux ratios, theoretical plates and feed throughput should be so adjusted as to take overhead at'least the major part of all the hydrocarbon components and mercaptans having a true boiling point below about F., while excluding therefrom substantially all compounds containing a thiophene ring, and substantially all hydrocarbon components having a true boiling point above about F. The term true boiling point is well understood in the art as referring to the boiling point of an individual component in the absence of vapor pressure-altering contaminants such as azeotrope formers and the like. To obtain the specified fractionation, column 21 may contain between about 10 and 60 actual plates, and overhead reux ratios of between about 1 and 15 may be employed, these factors being interrelated and balanced against the feed throughput, as will be understood by those skilled in the art.

The overhead from column 21 is much richer inolelins than the original feed. The overhead may containfor example between about 30% and 60% by volume of olens, where the feed contained only 1-5-40%. These oletinic compounds appear to display more tendency to azeotrope with like-boiling parafiins and naphthenes than with the thiophene compounds, as evidenced by the substantial absence of thiophene-ring compounds in the overhead. The complexity of the overhead may be appreciated when it is considered that the actual ASTM boiling range is ordinarily from about 80 to 180 F.

The overhead from column 21 is then transferred via line 23 to a debutanizer column 24 wherein a 90-100% butane stream is removed overhead via line 25. The bottoms from debutanizer 24, constituting valuable high anti-knock light ends from the gasoline, is then transferred via line 26 to a caustic washing column 27. Additional feed streams may also be included, as for example a light straight-run fraction admitted through linel 58. The object of treatment in column 27 is to reduce the mercaptan sulfur to the doctor sweet level,.and for this purpose, aqueous caustic scrubbing alone is generally insufcient; the addition of a solutizer is ordinarily required as for example methanol, ethanol, butanol, phenols, cresols or the like. The lightV gasoline stream enters the bottom of column 27 and flows upwardly countercurrently to a stream of aqueous methanol containing sodium hydroxide. The methanol component is preferably admitted to the column at a mid-point therein via line 28, and the aqueous caustic is preferably admitted near the top of the column through line 29. By admitting the methanol-free caustic near the downstream end of the column, any methanol which is dissolved in the gasoline is scrubbed therefrom and ows downwardly alongwith the aqueous caustic and dissolved mercaptides. The operation of such caustic scrubbing columns containing a solutizer is well understood in the art and hence need not be described in detail.

The caustic washed light gasoline is then taken ot overhead through line 30, washedwith water admitted through line 31 to a mixing valve 32, and then admitted. to a settling tank 33. Wash Water containing traces of alkali is withdrawn through line 34,. and the sweetened, light gasoline is then withdrawn. through line 35 and sent to a storage tank 36.

The spent caustic-aqueous-methanol from column 27 is withdrawn from the bottom thereof and transferred via line 37 to a caustic and methanol regeneration unit 38. The regeneration is conventional and need not be described in detail. It ordinarily involves a distillation to strip out a mixture of methanol, water and mercaptan as overhead, followed by condensation and phase separation to recover the bulkV of the mercaptans. The methanol-water phase is usually then scrubbed.' with the inconiing gasoline feedstock from line 26 to scrub out traces'of mercaptan, andthe thus-purified methanolwater is then recycled tocolumn 27 via line 28. 'Ihe aqueous caustic, stripped of mercaptans and methanol, is then recycled to the top Vof column 2.7 via line 29.

The bottoms from dehexanizer lcolumn 21 comprises the primary feedstock which is subjected to` catalytic hydrodesulfurization and reforming.` 'Ihis stock contains the great bulk of the refractorythiophene-type sulfur compounds. In order to eliminate such sulfur compounds it is necessary to treat the stock by catalytic hydrodesulfurization. To accomplish this the bottoms fraction in line 72 is admixed with recycle hydrogen from line 73, heated in preheater 39 to desulfurization temperatures, and passed via line 40 to catalytic desulfurizer 41, through which Ait flows in intimate contact with the cobalt-molybdate catalyst. 'Ihe preferred reac- Vtion conditions in desulfurizer 41 include temperatures between-about 625 and-875 F., pressures between about 200 and 5,000 p.s.i.g., hydrogen A-rates between about 200 and 5,000 s.c.f. per barrel of feed, and space velocities between about 0.5 and 20. The reactions occurring in desulfurizer 41 include the selective hydrocracking of sulfur compounds, nitrogen compounds, oxygen compounds, as well as a substantial saturation of the olefins present therein. There is ordinarily a net consumption of hydrogen amounting to betweenabout 50 and 500 s.c.f. per barrel of feed.

The productfrom desulfurizer 41 is withdrawn through line 42 and admitted to a hi-gh pressure separator 43 from which recycle hydrogen gas is withdrawn through line 44. Thevliquid productfrom high pressure separator 43 Vvis then transferred via line 45 to a low pressure separator 46 where dissolved light gases are flashed off through line 47 for use as fuel gas orotherwise as may lbe` desired. The liquid` product from separator 46 then constitutes the primary feedstock for the reformer, and is suliciently low in sulfur that it may be treated with such sulfur-sensitive reforming catalysts as platinumalumina, or platinum-silica, where the silica has been partially deactivated by steaming or otherwise, or other transitional metal catalysts.

In the particularmodication illustrated, the desulfurizedproduct from `separator 46 i's transferred via line 4 8 toV an intermediate fractionating column 49 wherein a heavy bottoms product constituting a refined stove oil'V is taken off through line 50. The overhead fromcolumn 49 ordinarily has a boiling range from about-150400 F., and this product is transferred Via line l'62-to reformer ,feed preheater 51, in admixture with-recyclehydrogenfadmitted through line V52. The preheated l'`feed-plus-hyd'rogen Ais vadmitted through `.line

53. and'ows downwardly-in contact with the catalyst infreformer "54. VThegpreferred catalyst in reformer 54 is` platinum-alumina, `i.e. activated alumina-containing supported thereon about 0.1% to 1.0% by'weight of platinum. Small amounts of chlorine or uorine may also be included on the catalyst. Other reforming catalysts may be employed as for example, chromia, nickel, cobalt-molybdate, rhodium, molybdena and the like. Allofthese `materials lare ordinarily supportedon Van adsorbent carrier such as activated alumina, aluminasilica, variousacid-treated clays,.or the like.V Normally, thereforming conditions include temperatures between about ,850 and`ll00 F.,pressures between about 100 and 2000 p.s.i.g., hydrogen 4rates between about 500y and 10,000 s.c.f. per barrel of feed, and space velocities between about 0.5 and l0. These conditions effect substantial dehydrogenation of naphthenes to aromatics, isomerizationof parans and olefins, cyclization of paraflins-and perhaps lother reactions, all resulting `in increasedV antiknock value'oftheproduct.

l`he -eluent from reformer 54 is then withdrawn :through/lineSS. and` admitted to, a l 1igl1 'pressure sepa'- rator 56. Recycle hydrogen gas from the reformer is recycled via lines 57 and 52 to the reformer unit. Inasmuch as the reforming operation results in a net make of hydrogen, the excess is bled off through line 73 and utilized in the hydrogen-consuming desulfun'zation reactor 41. It is desirable to maintain a hydrogen balance in the process, whereby sufcient hydrogen is synthesized in the reformer to balance the hydrogen consumption inthe desulfurizer. VTo accomplish this objective, sufiicient straight-run gasoline feedstock, obtained for example as bottoms from fractionatingV column 60, is admitted Via line 61 to the desulfurizer feed line 72. The straight-run gasoline is high in naphthenes and low in olefins, and hence consumes little hydrogen in the desulfurizer and synthesizes a disproportionately large amount in the reformer. By suitably adjusting the quanl tity of straight-run gasoline admitted through line 61,

in proportion to the cracked stockinline 72, it is possible to maintain the desired hydrogen balance;

,The removal of the highly olefinic, highly hydrogenconsuming, light ends in dehexanizer column 21, has a substantial beneficial effect onv the voverall hydrogen balance maintained in the reformer-desulfurizer combination. This is especially important to refiners whose renery balance must embrace the disposition of large quantitiesof high-sulfur, heavy crude oils, and hence thermally cracked gasolines, and wherein there is a limited supply of straight-run gasoline. In many instances, the thermallycracked gasolines available (which must be subjected to hydrodesulfurization before they can be successfully reformed into high octane naphthas) require the consumption of more hydrogen than the available straight-runA stocks will generate by reforming. The elimination of the highly olenicoverhead, and its treatment by caustic washing, hence accomplishes the dual objective of preserving the valuable anti-knock qualities of the oleiins contained therein, as well as reducing the hydrogen demand in the desulfurizer, thereby giving greater flexibility in the refinery balance, and permitting the treatment in desulfurizer 41, reformer 54, and caustic scrubber column .27, of a larger overall quantityV of cracked naphtha feedstock than could be processed through the A'desulfurizer-reformer combination alone,

using only the hydrogen available from reforming a givenI quantity of straight run gasoline. Even though theV netfhydrogen make from the reformer is not ernployed exclusively-in the naphtha desulfurizer, it is desirable to minimize hydrogen consumption in the desulfurizer, whereby any excess hydrogen from the reformer may be utilized for other purposes, as e.g. ammonia synthesis or `desulfurization of other feedstocks. Y In some cases, the use of straight-run stocks in the reformer may be eliminated altogether, the desulfurization and reforming reactions being in hydrogen balance as a result of the removal of the highly hydrogen-consuming light ends from the feed.

'The desulfurized, reformed, high-octane gasoline in separator 56 is transferred via line 65 to a low pressure separator 66, wherein light gases are flashed off through line 67 for use as 'fuel or otherwise. The final gasoline product is withdrawn through line 68 and transferred to storage tank 69. The gasoline product in storage tank 69 has high anti-knock quality, but is deficient in light ends 'required for adequate warm-up quality. Hence, the final gasoline is produced by blending suitable proportions of the light, desulfurized oleiinic stock from storage tank 36 via line ,70, and the final gasoline blend is transferred to ultimate tankage and storage via line 71.

The cobalt-molybdate catalyst employed in desulfurizer 41 comprisesa mixture of cobalt and molybdenum oxides wherein the molecular ratio of CoO to M003 is between about 0.4. and 5.0. This catalyst may be employed in unsupported form or, alternatively, Iit is preferably distendedon a suitable carrier such as alumina, silica, Zirconia, thoria, magnesia, titania, or any combination thereof. Of the foregoing carriersV it has been found that the preferred carrier material. is alumina, and especially alumina-containing about.38% by weight of silica. The supported catalyst may be prepared by impregnation with suitable soluble salts of cobalt and molybdenum followed by drying and calcining, or by coprecipitatronor co-pilling methods.` Suitable methods for preparing the catalysts are more specifically described in U.S.- Patents 2,369,432; 2,325,033; 2,486,361; 2,687,381; 2,393,288 and.2,499,255.

While cobalt-molybdate catalysts are preferred, other desulfurization catalysts may also be employed as for example molybdenum oxide, tungsten oxide, nickel oxide, tungsten-nickel sulides, or in general any of the transitional metal oxides or sulfides which are capable of effecting the selective hydrocracking of sulfur compounds with concomitant olefin hydrogenation under the conditions herein described. The following example is cited to illustrate the results obtainable in a typical process utilizing a refining sequence similar to that described in connection with the drawing. This example is illustrative only and is not to be construed as limiting in scope.

Example About 20,000 barrels per day of a Santa Maria Valley (California) crude oil containing 5.0% by weight of sulfur, 0.63 weight percent nitrogen, and having an API gravity of is subjected to delayed thermal coking whereupon there is produced 16,000 barrels of coker distillate, and 500 tons of coke. The coker distillate is fractionated to recover the 450 F. end-point pressure distillate, and the gas-oil residue is subjected to thermal cracking. The thermally cracked product is then fractionated to recover an additional quantity of 450 F. end-point pressure distillate. The combined stream of coker pressure distillate and thermal pressure distillate, containing 1.59% by weight of sulfur, is then carefully fractionated at an over-head true-boiling-point cut point of 185 F., to obtain anl overhead amounting to about 23% by volume of the feed to the column. This overhead. contains about 40% by volume of olefins, and after debutanizing, has an ASTM boiling range of 110-180 F., and contains 0.46% by weight of total sulfur.

The debutanized C5-C6 fraction is then subjected to countercurrent scrubbing with caustic-aqueous-methanol, and finally with aqueous caustic, yielding 1950 barrels of light gasoline containing 0.04% by weight of total sulfur and- 0.0002% ofl mercaptan sulfur, and having an F-l leaded (plus 3 ml. TEL) octane'rating of about 96. Had thisfraction been subjected to catalytic hydrodesulfurization and reforming, its leaded octane rating would be reduced to about 88.

The bottoms product from fractionation of the cornbined pressure distillates, having a boiling range of 200- 450 F. is then subjected to desulfurization at about 800 F. and 1500 p.s.i.g., with the addition of 3,000 S.C.F. of hydrogen per barrel of feed. The feedstock to the desulfurizer contains about 1.82% sulfur by weight. A liquid feed rate of about 1 volume per volume of catalyst per hour is employed.

The catalyst is acobalt molybdate type consisting essentially of 2% by weight of CoO and 10% by weight of M003 supported on 5% SiO2-95% A1203, the carrier in coprecipitated form. The dried SiO2-Al203 cogel is impregnated first with an ammoniacal ammonium molybdate solution, dried, heated to 1200 F. for 2 hours, impregnated secondly with an aqueous solution of cobalt nitrate, dried and heated to 1200 F. for 2 hours.

The eiuent from the desulfurizer is then fractionated torecover a desulfurized light product boiling between about 160-3 80 F. and containing about 0.005% sulfur. This product is mixed with about by volume of straight-run gasoline of 400 F. end point, and the mixture is supplied to the catalytic reformer operating at about 950 F., a pressure of 450 p.s.i.g., recycle hydrogen' ratesof about 4000. s.c.f. per barrel' of feed, and at a feed. rate of about.2.5 volumes of charge per volume of catalyst per hour. The catalyst is activated alumina. containing 0.2% by weight of impregnatedplatinum. Approximately 8,220 barrels of gasoline per day is produced from the reformer, about 6,850 barrels of which is derived from the cracked stock supplied to the desulfurizer. By blending the caustic extracted light gasoline with the reformate gasoline, 10,170 barrels per day of full-range, doctor-sweet gasoline is obtained having a leaded octane rating of 97.3, and containing less than 0.01% sulfur.

By omitting the fractionation step, and' sending the light ends of the gasoline through the desulfurizer and reformer under the conditionsy of this example, substantially the same ultimate liquid` yield of gasoline is obtained, wherein however the leaded octane rating is about 95.4. To compensate for this octane loss, more severe' yield is then about 2.0% less, resulting in an ultimatev recovery of 9,967 barrelsl of gasoline of 97.3' leaded octane rating.

The foregoing example may be modified by employing different catalysts at substantially the same reaction conditions, or the reaction conditions may be modified using the same catalysts to obtain the same results. The foregoing disclosure is hence not to be considered as limiting since many variations may be made by those skilled in the art without departing from the scope or spirit of the following claims.

I claim:

1. A process for desulfurizing and reforming a fullrange, high-sulfur, thermally cracked naphtha, which comprises fractionating said naphtha to recover a light overhead fraction rich in olelins and a heavy bottoms fraction constituting substantially the entire remainder of said naphtha, said light fraction containing the major part of all the hydrocarbon components and mercaptans having a true boiling point below about 180 F., said light fraction being substantially free from (l) compounds containing a thiophene ring and (2) hydrocarbon components having a true boiling point above about F., subjecting said light fraction to aqueousalkaline extraction to extract therefrom said mercaptans, subject- 1 ng said heavy fraction to catalytic hydrodesulfurization 1n the presence of hydrogen and a cobalt molybdate catalyst at temperatures between about 625 and 875 F., subjecting the desulfurized heavy fraction to catalytic reforming in the presence of hydrogen and a reforming catalyst comprising as an essential element an active metal selected from groups VIB and VIII of the periodic table, and thereafter blending portions of the reformed heavy gasoline from said reforming step with a portion of sald caustic-washed light fraction to obtain a desulfurized full-range gasoline of higher anti-knock quality than would be produced by subjecting said full-range cracked naphtha to hydrodesulfurization and reforming under the same conditions.

2. A process as defined in claim 1 wherein sufficient stralght-run gasoline is included with said desulfurized heavy fraction supplied to said reformer to generate thereln sufiicient hydrogen to balance the hydrogen consumed in said hydrodesulfurization step, and sufficient of said generated hydrogen is passed to said hydrodesulfurization to supply the hydrogen therein consumed; 3. A'process as defined in claim 1 wherein said reformmg catalyst is activated alumina containing a minor proportion of platinum.

4. A process for desulfurizing and reforming a fullrange, |high-sulfur, thermally cracked naphtha, which comprises fractionating said naphtha to recover a light overhead fraction rich in oleius and a heavy bottoms fraction constituting substantially the entire remainder of said naphtha, said light fraction containing the major part of all the hydrocarbon components and mercaptans having a true boiling point below about 180 F., said light fraction being substantially free from (1) compounds containing a thiophene ring and (2) hydrocarbon components lhaving a true boiling point above about 190 F., subjecting said light fraction to aqueous-alkaline extraction to extract therefrom said mercaptans, subjecting said heavy fraction to catalytic hydrodesulfurization at a temperature between about 625 and 875 F. in the presence of hydrogen and a catalyst selected from the group consisting of the oxides and sullides of the transitional metals, subjecting the desulfurized heavy fraction to catalytic reforming in the presence of hydrogen and a reforming catalyst comprising as an essential element an active metal selected from groups VIB and VIII of the periodic table, and thereafter blending portions of the reformed heavy gasoline from said reforming step with a portion of said caustic-washed light fraction to obtain a desulfurized. full-range gasoline of higher anti-knock quality than would be produced by subjecting said fullrange cracked naphtha to hydrodesulfurization and reforming under the same conditions.

5. A process for refining a heavy crude oil rich in sulfur compounds which comprise passing said crude oil into a cokingl zone maintained at a temperature between about 800 and 1100 F. wherein said crude oil is converted to coke, gases, and a coker distillate having an increased ratio of hydrogen to carbon, separating a naphtha fraction and a higher boiling fraction from said coker distillate, passing said 'higher boiling fraction through a thermal cracking zone, withdrawing cracked products from said thermal cracking zone, separating from said cracked products a naphtha fraction and a higher boiling fraction, combining said coker distillate naphtha with said thermally cracked naphtha, subjecting the combined naphthas to fractional distillation to recover a light overhead fraction rich in olefins and a heavy bottoms fraction constituting substantially the entire remainder of said combined naphthas, said light fraction containing in major part of al1 the hydrocarbon components and mercaptans having a true boiling point below about 180 F., said light fraction being substantially free from (1) compounds containing a thiophene ring and (2) hydrocarbon components having a true boiling point above about 190 F., subjecting said light fraction to aqueous-alkaline extraction to extract therefrom said mercaptans, subjecting said heavy fraction to catalytic hydrodesulfurization in the presence of hydrogen and a cobalt molybdate catalyst at a temperatures between about 625 and 875 F., subjecting the desulfurized heavy fraction to catalytic reforming in the presence of hydrogen and a platinum reforming catalyst, and thereafter blending portions of the reformed heavy naphtha from said reforming step with a portion of said causticwashed light fraction to obtain a desulfurized full-range naphtha of higher anti-knock quality than would be produced by subjecting said combined full-range cracked naphthas to hydrodesulfurization and reforming under the same conditions. l

6. A process as dened in claim 5 wherein suicient stright-run gasoline is included with said desulfunzed heavy fraction supplied to said reformer to generate therein suliicient hydrogen to balance the hydrogen consumed in said hydrodesulfurization step, and suicient of said generated hydrogen is passed to said hydrodesulfurization to supply the hydrogen therein consumed.

7. A process as defined in claim 5 wherein said cobalt molybdate catalyst is supported on a carrier consisting of activated alumina containing a minor proportion of coprecipitated silica.

8. In a combined catalytic desulfurization and catalytic reforming process, wherein a thermally cracked naphtha is first subjected to hydrogenative desulfurization in the presence of a cobalt molybdate catalyst, and thereafter subjected to dehydrogenative reforming in the presence of a platinum-alumina catalyst, and wherein the hydrogen consumed in said desulfurization reaction is derived eX- clusively from said reforming step, and whenein an amount of straight-run gasoline is supplied to said reforming zone suflicient only to generate a net hydrogen make suicient to supply the hydrogen consumption in said desulfurization reaction, the improved method of minimizing hydrogen consumption in the desulfurization reaction and thus the amount of straight-run gasoline which must be supplied to said reforming zone, which comprises first separating from the full-range cracked naphtha supplied to said desulfurization zone a highly olefinic light fraction boiling substantially within the range of about -18031:., said light fraction being substantially free from compounds containing a thiophene ring, subjecting said light fraction to scrubbing with an aqueous caustic solution to extract mercaptans therefrom without affecting the olens contained therein, and reblending the sweetened light gasoline from said caustic scrubbing step with the reformed gasoline from said reforming step.

9. A process as defined in claim 8 wherein said cracked naphtha comprises a coker distillate boiling between about 80 and 450 F.

References Cited in the le of this patent UNITED STATES PATENTS 2,025,255 Taylor et al Dec. 24, 1935 2,324,165 Layng et al July 13, 1943 2,691,623 Hartley Oct. 12, 1954 2,763,358 Linn et al Sept. 18, 1956 OTHER REFERENCES Eagle et al.: Industrial and Engineering Chemistry, vol, 42, No. 7, July 1950 (pp. 1294-1299 relied on). 

1. A PROCESS FOR DESULFURIZING AND REFORMING A FULLRANGE, HIGH-SULFUR, THERMALLY CRACKED NAPHTHA, WHICH COMPRISES FRACTIONATING SAID NAPHTHA TO RECOVER A LIGHT OVERHEAD FRACTION RICH IN OLEFINS AND A HEAVY BOTTOMS FRACTION CONSTITUTING SUBSTANTIALLY THE ENTIRE REMAINDER OF SAID NAPHTHA, SAID LIGHT FRACTION CONTAINING THE MAJOR PART OF ALL THE HYDROCARBON COMPONENTS AND MARCAPTANS HAVING A TRUE BOILING POINT BELOW ABOUT 180*F., SAID LIGHT FRACTION BEING SUBSTANTIALLY FREE FROM (1) COMPOUNDS CONTAINING A THIOPHENE RING AND (2) HYDROCARBON COMPONENTS HAVING A TRUE BOILING POINT ABOVE ABOUT 190* F., SUBJECTING SAID LIGHT FRACTION TO AQUEOUS- ALKALINE EXTRACTION TO EXTRACT THEREFROM SAID MERCAPTANS, SUBJECTING SAID HEAVY FRACTION TO CATALYTIC HYDRODESULFURIZATION IN THE PRESENCE OF HYDROGEN AND CAOBALT MOLYBDATE 